The present invention relates to a method of bright electroplating tin-lead alloys, which is characterized by using hydroxyalkyl sulfonates as the commonly soluble complex salts of divalent tin and lead, and by using reaction products of acetaldehyde with O-toluidine as additives to the solution containing the above complex salts, thereby providing tin-lead alloy electrodeposits having desirable or excellent brightness, without exhausting poisonous chemicals which cause pollution.
Recently an electroplate of tin-lead alloy has been widely utilized on electric and electronic parts or elements as coating to improve soldering and for etching-resistoring; particularly a bright electroplate is admired.
At present, the plating solution containing borofluorate or phenol sulfonate is used for industries. But both of them contain poisonous chemicals which cause pollution in waste solution.
Namely, when using borofluorate, the drainage is contaminated with fluorine, a component of borofluoric acid, which is very poisonous and; when using aromatic sulfonates such as phenolsulfonate, the drainage is contaminated with phenols and phenolic compounds which cause public pollution and cyclic compounds containing benzene, which are chemically and biologically irresolvable.
Although these chemicals can be treated by a higher technique of resolvement, much cost is needed for equipment and treatment.
From the viewpoint of pollution as stated above, when using phenol sulfonates which are les poisonous that borofluorates, less bright electrodeposits may be obtained in the beginning of plating or in barrel-plating when electric current density is low.